1. Field of the Invention
The present invention relates to a photoelectric conversion device and a method for manufacturing a photoelectric conversion device.
2. Description of the Related Art
Japanese Patent Laid-Open No. 2005-167187 (hereinafter referred to as PTL 1) discloses an imaging device having a plurality of sensor cells. Each sensor cell has a photodiode including an accumulation well and a deep charge collection diffusion region. The accumulation well is relatively shallow in the depth direction of the substrate and is relatively wide in the horizontal direction. The deep charge collection diffusion region is located roughly in the center of the accumulation well. The deep charge collection diffusion region reaches an appropriately deep position in the depth direction, and is formed only in a relatively narrow region with respect to the horizontal direction. According to such a configuration, the collection efficiency of charges can be prevented from decreasing.
According to PTL 1, in the step of ion implantation for forming the accumulation well and in the step of ion implantation for forming the deep charge collection diffusion region, impurities of the same conductivity type are implanted into the same region. Specifically, in FIG. 4 (D) of PTL 1, it is disclosed to form the deep charge collection diffusion region (31 of FIG. 4 of PTL 1) by ion implantation. The distribution of boron ions implanted by this ion implantation has a peak at a depth of about 0.2 micrometers. In FIG. 5 (C) of PTL 1, it is disclosed to form an accumulation well (4 of FIG. 5 of PTL 1) by ion implantation. The distribution of boron ions implanted by this ion implantation has a peak at a depth of about 0.2 micrometers. Thus, impurities of the same conductivity type are implanted such that peaks of concentration distribution are located at the same depth. Two masks (31a of FIG. 4 of PTL 1, and 4a of FIG. 5 of PTL 1) used in the two steps of ion implantation have openings in the same region.